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43L Overheating Problem

J

jpfister

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"I am workign on a 4.3L in a 1

"I am workign on a 4.3L in a 1991 Sea Ray and running into what I think is an overheating problem. This was a salt water boat, and now in fresh water. The water manifolds, engine water pump, thermostat, etc. have been replaced. Now when running for 30min., the temp gage seems to lose the reading and the engine seems to get very hot end will loses all power. The water pump on the outdrive looks OK. I am at a total loss, does anyone have an idea?"
 
"the temp gage seems to lo

"the temp gage seems to lose the reading"

Make sure you are using a known good gage and that you truely have an engine temp problem. That wouldnt explain the loss of power though.
 
"Sounds like an elctrical prob

"Sounds like an elctrical problem coincident to both the temp gage and the ingnition system...
maybe a ground or short somewhere on the engine wiring harness.
Is the engine really getting hot? Check with a hand held infra-red thermometer, which is a MUST-HAVE for troubleshooting overheating problems. It let's you know what you have, not what a very inaccurate gage on the dash is telling you."
 
"JP, There is a test for wate

"JP, There is a test for waterpump impeller output. It is the amount of water pumped are a given RPM over a given time. This will allow you to confirm or deny the waterpump as the suspect. You can find it in a good Mercruiser manual."
 
"I just worked on my 4.3 this

"I just worked on my 4.3 this summer. I had to polish the inside of the T'stat tower with a grind stone using a dremel--one versatile tool--to remove the scale and rust to put in the new T'stat.

Wether you are using earmuffs with strong water pressure or lake water, all of the manifolds should be tepid or slightly warm to touch when the engine is at 140 deg. (my 87 calls for 140).

Using muffs won't tell you the impeller cond. A quick dry land test is to use a 1/4 barrell plastic beer tub full of water and lower the O/D into it. You might have to pull the prop to fit. Keep a hose running into the tub. The engine should run at the spec. temp. If not; time to replace the O/D pump and hose and while you are at it, lube the drive shaft U-joints and consider replacing the bellows if not done in the past 5 years.

Are the check valves operating in the top of the diverter T ? If the hoses on the T'stat tower are switched, the temp may read higher. The top hoses go to the top exhaust man. risers and the hose should be cool to touch. The lower hoses go to the bottom mans. and will be warm to touch.

Change the sending unit and the wire connector since it was in salt and the probe end is copper. My reading was off some and I pulled mine out and found a layer of rust and crap adhered to it--NAPA for $13. Instant temp readings now.

The only thing that should be hot to touch is the upper part of the thermostat tower where it mixes hot engine water with cool lake water and sends it to the exhaust mans.

Is the O/D water hose (back of the engine) kinked? (or the one in the O/D) You can pull it off at the inside of the transom and run a garden hose on max into it (engine off) and check for water passage flow to the O/D. If water tries to back flush out the hose end you are holding, the power steering cooler may be plugged somewhat. Pull off both hoses and shine a light thru it or back flush it from the engine circulating pump hose.

Good luck."
 
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